Motion Profile and System Motion Parameters
In general, the need to control the velocity of an elevator is well known. Reference is had, for example, to assignee's U.S. Pat. No. 4,751,984 of Walter L. Williams, Donald G. McPherson and Arnold Mendelsohn entitled "Dynamically Generated Adaptive Elevator Velocity Profile" issued Jun. 21, 1988, as well as to the art cited therein, the disclosure of which are incorporated herein by reference.
As noted in the Williams et al patent, automatic elevator operation involves the control of elevator velocity with respect to zero or stop, at the beginning and the end of a trip, to speeds therebetween, which minimize trip time while maintaining comfort levels and other constraints. The time change in velocity for a complete trip is termed the car's "velocity" or "motion profile." Automatic elevator control further requires control of the distance travelled during a trip in order to accomplish a precision stop at the destination floor. See also the said '401 patent.
Thus, in an elevator system a car is typically moved from one location to another with an acceptable motion profile and system motion parameters which involve acceptable car "jerk" and acceleration. The particular motion profile and motion parameters selected represent a compromise between the desire for "maximum" speed and, inter alia, the need to maintain acceptable levels of comfort for the passengers.
Maximum speed, of course, allows the car to get from floor location to floor location in as short a time as possible, so as to minimize the service time and the waiting time of passengers and improve handling capacity. Maximum speed thus achieves the best service possible, but then this must be tempered with the need for acceptable limits of passenger comfort. Thus, for example, with respect to the latter constraint, too great a rate of acceleration or deceleration produce unacceptable passenger discomfort.
In view of the necessity of this compromise between minimizing service time and the need for passenger comfort, an acceptable motion profile governing the movement of each elevator car as it moved from one location to another was included in the design of an elevator system and remained fixed during the operation of the system. Such acceptable profile varies from marketing territory to marketing territory (e.g. the North American market generally places greater emphasis on speed, while the Pacific market places greater emphasis on comfort) or indeed from customer to customer, but once set in the system the profile remains fixed during the normal operation of the system.
Thus, regardless of which motion profile was ultimately decided upon, it was typically pre-selected and fixed prior to starting the operation of the system. These fixed motion profile parameters provided a certain level of performance and ride quality that would stay the same for the rest of the elevator life, unless changed by a mechanic or an adjuster at the job site. If the pre-set parameters favored ride quality, then the relatively low acceleration, jerk and deceleration rates of the profile diminished performance, and vice-versa. The system therefore suffered in one way or another from this compromise on a relatively fixed or "permanent" basis.